In general, the operation of electronic devices such as monitors, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. Such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed “electromagnetic interference” or “EMI”. EMI is known to interfere with the operation of other proximate electronic devices. “EMI” is used herein interchangeably with the term “radio frequency interference” (“RFI”).
For attenuating EMI effects, suitable EMI shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other “target” devices from other source devices. Such shielding is provided as a barrier which is interposed between the source and the other devices, and most often is configured as an electrically conductive and grounded housing or other enclosure which surrounds the EMI generating circuitry of the source device. However, when such circuitry is contained within the confined space of an enclosure, it often is necessary to provide a cooling or ventilation means to dissipate the heat which is generated by the circuitry. Most enclosures therefore are formed with one or more air intake and/or exhaust openings or ports for natural or forced convective circulation of air between the interior of the enclosure and the ambient environment.
Left uncovered, such openings would represent a discontinuity in the surface and ground conductivity of the enclosure, with the result of a decrease in the EMI shielding effectiveness of the enclosure. Accordingly, shielded vent panels have been used for covering the openings in a manner which allows ventilation of the enclosure while electrical continuity, i.e., grounding, across the vent opening is maintained.
In basic construction, such vent panels, which are sized to span the corresponding opening in the enclosure, conventionally are formed from a sheet of a porous, electrically-conductive shielding media, i.e. a vent opening, and an electrically-conductive frame member configured to support the media by circumscribing the outer periphery thereof. The media, which may be a honeycombed-structured or other cellular structured conductive material, is received in or is otherwise attached to the frame, which typically is provided as an extruded aluminum, stainless steel, Monel, or other metals. The frame, in turn, may be fastened to the enclosure over the opening thereof with screws or the like, and a compressible, electrically-conductive seal or gasket is optionally provided for improved electrical contact between the frame and the enclosure.
In view of the proliferation of electronic devices, it is to be expected that continued improvements in EMI shielded vent panels would be well-received by the industry, and particularly by the designers of enclosures for personal computers, file servers, telecommunication equipment, and similar systems which now operate at frequencies of 500 MHz or more. Indeed, as the processing speeds of electronic devices continue to increase with the attendant generation of higher frequency EMI radiation and greater heat output, enclosure designers are faced with the seemingly competing requirements of providing both adequate ventilation and effective EMI shielding. In such applications, a honeycomb shielding media, often may be preferred over other media as it is known to provide effective EMI shielding at higher frequencies with less restriction to air flow.